Trisomy 18: Details on Bella Santorum’s genetic disorder

Isabella, or "Bella" Santorum, Rick Santorum's 3-year-old daughter, was born with Trisomy 18 — a lethal genetic disorder. She was hospitalized this past weekend after contracting pneumonia, which likely arose due to the chromosomal defect. Bella also had rough 36-hour battle with pneumonia in January.

Alluding to his daughter's illness, Santorum suspended his campaign for presidential Tuesday afternoon at an event in Pennsylvania.

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Santorum's campaign has inadvertently brought attention to his daughter's rare genetic disorder. Here is an explaination on what Trisomy 18 is.

It means that the afflicted person has developed three copies of the 18th chromosome instead of two. The disorder, also known as Edwards syndrome, can lead to a myriad of developmental problems that affect the brain and other vital internal organs.

According to the National Institute of Health, other symptoms can include:

Clenched hands

Crossed legs (preferred position)

Feet with a rounded bottom (rocker-bottom feet)

Low birth weight

Low-set ears

Mental deficiency

Small head (microcephaly)

Small jaw (micrognathia)

Underdeveloped fingernails

Undescended testicle

Unusual shaped chest (pectus carinatum)

According to the Trisomy 18 foundation, Edwards occurs in one out of every 3,000 live births. Other experts put the figure at one out of every 5,000 to 10,000 births.

Researchers note that Edwards is “similar in etiology” to down syndrome, which is caused due to a defect in the 21st chromosome. However, Trisomy 18 is much more severe.

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Robert Marion, chief of genetics and developmental medicine at the Children’s Hospital at Montefiore Medical Center in the Bronx, New York, told The Washington Post "almost half the children born with the condition die within the first three months of life, 90 percent die in the first year, and the 10 percent who survive have severe developmental problems.”

The disorder can be diagnosed prenatally, Marion noted, and most are usually terminated. 

Males and females are equally vulnerable to the disorder, but “those who survive are almost always girls,” said Marion. “The reason for this is that the condition is more lethal in boys, who die intrauterinely.”

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While it isn't uncommon for children with Trisomy 18 to contract pneumonia, as Marion explained to the Post, at three years old Bella is already an exception, Dr. Ronald Crystal, chair of genetic medicine at Weill Medical College of Cornell University in New York City, told ABC news.

The oldest child Marion has tracked with Edwards is only 13 years old.